The present invention relates to a display apparatus using a matrix display panel such as a liquid crystal panel, and particularly to a scanning conversion display apparatus having a matrix display panel suitable for displaying a picture with a larger number of scanning lines as compared with the number of displayed scanning lines.
Among various color television systems, three systems including NTSC system, PAL system and SECAM system have dominated the world markets. Recently, the "high-vision" system which offers high quality pictures entered a phase of experimental broadcasting, and the variety of color television systems is going to increase.
In order to reproduce a picture correctly on a matrix display panel, the television signal must be processed to meet the respective television system and a matrix display panel having a proper number of pixels for producing the prescribed number of scanning lines of the television system must be used. In general, a matrix display panel, with the number of pixels being set to suit the number of scanning lines of one system, cannot be used directly to display a picture of another system having a different number of scanning lines.
As a means of overcoming this situation, a circuit arrangement, described in Japanese Patent Publication No. 62-533989, for driving 240 scanning electrodes of a NTSC-based matrix panel includes a dummy flip-flop inserted in each of five-stage shift register groups connected to the scanning electrodes with the intention of displaying, by line extraction, a PAL-based picture having 287 scanning lines in each field. For a NTSC-based picture, the dummy flip-flops in the scanning electrode drive circuit are not used and the whole 240-stage shift register operates to display the picture.
An alternative sophisticated method is designed to store a picture in a memory temporarily and the number of scanning lines is converted through the video signal processing.
The above-mentioned conventional technology described in the patent publication 62-53989 necessitates a special scanning electrode drive circuit (will be termed "vertical scanning circuit" hereinafter) including dummy flip-flops. A usual vertical scanning circuit made up of simple shift registers without dummy flip-flops cannot display a picture formed of scanning lines more in number than the displayed scanning lines (number of vertical pixels) of the panel. The method of storing a picture temporarily in the memory for processing the video signal involves a large-scale circuit arrangement and it is not suitable for a compact planar television set or the like.